1. Technical Field
The present invention relates to a display device.
2. Discussion of the Related Art
Liquid crystal displays (LCDs) are among the most widely used flat panel displays. For example, LCDs are commonly found in a variety of electronic devices such as televisions, laptop computers, personal digital assistants, cell phones and digital cameras.
An LCD includes a pair of panels provided with field-generating electrodes, such as pixel electrodes and a common electrode, and a liquid crystal (LC) layer interposed between the two panels. The LCD displays images by applying voltages to the field-generating electrodes to generate an electric field in the LC layer that determines the orientations of LC molecules therein to adjust polarization of incident light.
The LCD also includes switching elements connected to respective pixel electrodes, and a plurality of signal lines such as gate lines and data lines for controlling the switching elements and thereby applying voltages to the pixel electrodes.
LCDs generally include vertical alignment (VA) mode LCDs and patterned vertically aligned (PVA) mode LCDs. In VA mode LCDs, a longitudinal axis of an LC molecule is perpendicular to upper and lower panels in the absence of an electric field, and thus the contrast ratio is large and the reference viewing angle is wide. The reference viewing angle is defined as a viewing angle making a contrast ratio equal to 1:10 or as a limit angle for the inversion in luminance between grays, for example.
In the VA mode LCD, a wide viewing angle is achieved by forming a cutout in a field generating electrode, and forming a protrusion above or below the field generating electrode. Since the cutouts and the protrusions can determine the directions in which the LC molecules are inclined, the tilt directions can be distributed into various directions by appropriately arranging the cutouts and the protrusions to increase the reference viewing angle.
In the VA mode LCD, side visibility is inferior to front visibility. For example, in the case of a PVA mode LCD having cutouts, an image becomes brighter toward the side so that there is no difference in luminance among high gray levels, and in a severe case, the image looks crumbled.
In an LCD, to make the lateral visibility close to the front visibility, a method in which one pixel is divided into two sub-pixels and the two sub-pixels are applied with different voltages to obtain different transmittance has been proposed.
In one method, after dividing one pixel into two sub-pixels and capacitively coupling the two sub-pixels with each other, a voltage is directly applied to one sub-pixel and a drop in voltage is caused in the other sub-pixel by the capacitive coupling to make the voltages of the two sub-pixels different from each other, and thus make the transmittances of the two sub-pixels different from each other. However, since one of the voltages of the two sub-pixels is decreased in this method, the overall transmittance may be reduced.
In another method, the number of gate lines or data lines may be increased to apply the different voltages to the two sub-pixels. However, if the number of gate lines or data lines is increased, the aperture ratio of the LCD is reduced.
Accordingly, there exists a need for a technique of improving lateral visibility of an LCD without a reduction in transmittance or aperture ratio.